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The GPS WGS84 coordinate system, often referred to simply as WGS84, is a widely used global geodetic reference system and coordinate system for specifying locations on the Earth’s surface. WGS84 stands for “World Geodetic System 1984,” and it was developed and is maintained by the United States Department of Defense. It serves as the foundation for global positioning systems (GPS) and various mapping and navigation applications worldwide.

Earth Model: WGS84 assumes that the Earth is an ellipsoid, a slightly flattened sphere, to represent the Earth’s shape accurately. This ellipsoid is known as the WGS84 ellipsoid, and it approximates the Earth’s shape very closely.

Coordinate Representation: WGS84 uses a system of latitude and longitude to specify locations on the Earth’s surface. Latitude measures north-south position, while longitude measures east-west position. Latitude values range from -90° (South Pole) to +90° (North Pole), and longitude values range from -180° to +180°.

Datum: WGS84 is based on a specific reference point, known as the geodetic datum. This datum is a mathematical model that defines the reference point, the shape of the Earth’s ellipsoid, and the orientation of the coordinate axes. The WGS84 datum was updated in 1984 to improve accuracy and alignment with other global geodetic systems.

Accuracy: WGS84 is designed to provide a highly accurate and consistent reference system for global navigation and positioning. It is used as a standard for GPS devices and mapping systems to ensure that locations are specified consistently across the globe.

Compatibility: WGS84 is widely adopted and accepted as the de facto standard for geospatial data interchange and coordinate reference. Many geographic information systems (GIS), mapping software, and GPS devices use WGS84 as their default coordinate system.

Coordinate Transformations: When dealing with maps or data in different coordinate systems, it may be necessary to perform coordinate transformations to convert between WGS84 and other local or regional coordinate systems.

Elevation Data: In addition to latitude and longitude, WGS84 also includes a system for specifying elevation or height above or below the reference ellipsoid. This is typically represented in meters.

It’s important to note that while WGS84 provides a globally consistent reference system, the Earth’s surface is not perfectly smooth, and its shape may vary slightly in different locations due to factors such as local gravitational anomalies. Therefore, in certain precision applications, more localized geodetic datums and coordinate systems may be used to account for these variations. However, for most everyday GPS and mapping purposes, WGS84 coordinates are sufficient and widely used.

The difference between WGS84 ellipsoid height and orthometric height lies in how they measure elevation or height above the Earth’s surface, and they are used in different contexts:

WGS84 Ellipsoid Height (Geodetic Height):

WGS84 ellipsoid height, also known as geodetic height, is a measurement of elevation above the WGS84 reference ellipsoid. This reference ellipsoid represents the idealized shape of the Earth. It is measured along the normal to the ellipsoid’s surface. In simple terms, it’s the height you would get if you used a GPS receiver to measure your elevation above the mathematical model of the Earth’s surface. WGS84 ellipsoid height is often used in geodesy, surveying, and global positioning systems (GPS) to establish precise coordinates and positions.

Orthometric Height (Geopotential Height):

Orthometric height, also known as geopotential height or simply “height above sea level,” is a measurement of elevation above a geoid or a reference equipotential surface (approximately sea level). The geoid is a surface that represents the mean sea level of the Earth’s oceans, taking into account the effects of gravity and the Earth’s irregular shape caused by variations in gravity due to differences in mass distribution (such as mountains and ocean trenches).
Orthometric height is what we typically think of as elevation when we see elevation markings on maps, and it’s the height used in practical applications like determining the height of mountains, the depth of valleys, or elevations on topographic maps. To obtain orthometric heights, specialized equipment like leveling instruments or GNSS receivers with access to geoid models is required because they take into account the local variations in the Earth’s gravity field.

In summary, the key difference is that WGS84 ellipsoid height is a measurement above the mathematical model of the Earth’s surface (the ellipsoid), while orthometric height is a measurement above the geoid (mean sea level). Orthometric heights are typically used for everyday elevation references, as they are more relevant for practical applications, while WGS84 ellipsoid heights are used in geodetic and surveying contexts where precise positioning and calculations are required. When working with elevation data, it’s essential to understand which type of height you are dealing with and apply the appropriate corrections if necessary to convert between the two.